1. Field of the Invention
The present invention relates to an insulation-coated wire comprising a semiconductive layer, more particularly, to an insulation-coated wire with an excellent partial discharge resistance property.
2. Related Art
In recent years, it has been the mainstream that a motor, a generator and the like employed for vehicles are driven by an inverter drive at a high voltage for improving energy-saving, dynamic performance, or the like.
An enamel-coated wire has been used as the insulation-coated wire used for a coil of such a motor or generator. However, if an overvoltage (inverter surge) occurs in the motor or generator at the time of driving the motor or generator by the inverter drive at the high voltage, a partial discharge may occur in an insulating layer of the enamel wire due to this inverter surge. As a result, there is a high risk that the insulating layer is deteriorated or eroded, thereby causing an insulation breakdown. In addition, when the drive voltage of the motor or generator is increased, the risk of causing the partial discharge in the insulating layer becomes high.
As an approach for suppressing the occurrence of the partial discharge in the insulated wire, a technique of containing carbon particles in a resin coating composing the insulating layer to provide a semiconductive layer as the insulating layer, in order to prevent the partial discharge in the insulating layer has been known. For example, Japanese Patent No. 3077982 (JP-B-3077982), Japanese Patent Laid-Open No. 2007-5174 (JP-A-2007-5174), Japanese Patent Laid-Open No. 2005-285755 (JP-A-2005-285755), and Japanese Patent Laid-Open No. 2005-251573 (JP-A-2005-251573) disclose such a technique.
Further, as an approach for preventing the insulation breakdown, a technique of mixing an inorganic filler such as aluminum oxide, silica, in the resin coating composing the insulating layer, thereby preventing the deterioration or erosion of the insulating layer even though the partial discharge occurs in the insulating layer has been known. For example, Japanese Patent Laid-Open No. 2001-307557 (JP-A-2001-307557) and Japanese Patent Laid-Open No. 2005-112908 (JP-A-2005-112908) disclose such a technique.
However, in the technique of containing the carbon particles in the resin coating composing the insulating layer, there is a disadvantage in that a viscosity of the resin coating may be remarkably increased due to the carbon particles. When the resin coating with the high viscosity is coated and baked on the conductor, unevenness or irregularity in a thickness of the semiconductive layer is caused, so that the semiconductive layer having a uniform thickness and a smooth surface cannot be obtained.
In the technique of mixing the inorganic filler in the resin coating composing the insulating layer, thereby suppressing the deterioration or erosion of the insulating layer in order to prevent the insulation breakdown, an effect of increasing a deterioration resistance property of the insulating layer against the partial discharge can be expected. However, since this technique does not suppress the occurrence of the partial discharge per se, there are various remaining problems, e.g. long-period reliability for maintaining the deterioration resistance property for a long period against the partial discharge, generation of noise due to the partial discharge.